The invention relates to the agglomeration of mineral-derived fines, and more particularly to the agglomeration of oil shale fines.
Minerals are solid crystalline elements or compounds, often highly valuable, which are mined or quarried and then fashioned into desired products. The mining and working of minerals results in the formation of dust or particulate matter known as fines. Fines are now being recognized as detrimental to the environment and the health of persons working with these materials. Moreover, the loss of the mineral content of fines results in the less than total utilization of the earth's finite resources.
The effects of fines on the environment are manifold. Particulate matter is easily carried by air currents high into the atmosphere, only later to be deposited on vegetation and housing, often bringing with it undesirable toxic and reactive substances which are harmful to vegetation and may cause accelerated aging of roofing and protective paint applied to housing. Fines also present a problem in the disposal of spent mineral wastes. The small size of these particles may destabilize any landfill site in which they are deposited; additionally, fines may leach out of the landfill site, thereby damaging the environment far beyond the geographical confines of the landfill site.
Occupational health hazards have long been recognized as being associated with the inhalation of dust by coal miners and steel workers. A disease state known as "pneumoconiosis" has been identified which encompasses health problems having their etiology in dust inhalation. Pneumoconiosis, or dust on the lungs, has been found to induce lesions on the bronchioles, permanent dilation of small airways in the lungs, and loss of elasticity of lung tissue. Any toxic nature of inhaled mineral-derived dust would dramatically increase the health hazards accompanying inhalation. For example, is arsenic is present in inhaled dust, prolonged inhalation could result in arsenic poisoning.
The fines which are produced by mining, working, or transporting materials can represent a substantial fraction of the potential value of the minerals removed from the earth. For example, in the crushing of oil shale into small particulates, a necessary step before retorting to extract the hydrocarbon content, up to 20 percent of the weight of the oil shale is ground into fines. A loss of these proportions of oil shale represents a significant inefficiency in the extraction of hydrocarbons therefrom, and runs counter to the pressing need for the conservation of natural resources.
The patent literature has recognized environmental, health, and conservation problems related to the production of fines in the mining and working of minerals. United Kingdom Pat. No. 677,279 describes spraying dusty areas with aqueous liquids containing alkyl benzene sulphonates in which the alkyl group contains from 10 to 12 carbon atoms. U.S. Pat. No. 4,067,818 issued to Marin discloses a formulation for laying dust containing up to 2 percent by weight of an alkyl orthoxylene sulphonate.
The present energy shortage has brought about renewed interest in oil shale, a sedimentary mineral formation comprising marlstone deposits with layers containing an organic polymer called kerogen which upon heating decomposes to produce liquid and gaseous hydrocarbon products capable of being refined into a useful energy source. Oil shale is mined by conventional techniques, including drilling and blasting of the mineral formation. The mined oil shale is crushed to reduce the size of the shale to aid in material handling and to reduce the time for retorting. Unfortunately, in the above processes there is little or no control over the resulting size distribution of shale, thereby leading to the formation of a considerable quantity of oil shale fines.
A need remains for a simple inexpensive method for controlling mineral-derived fines. Such a method would preferably be useable under the adverse condition found in the mining and working of minerals.
Accordingly, it is an object of the present invention to provide a method for agglomerating mineral-derived fines.
Another object is to provide a method for agglomerating oil shale-derived fines.
These and other objects and advantages of the invention will be apparent to those skilled in the art in view of the following description of the invention.